This invention relates to solar batteries for time pieces, and more particularly to solar batteries in which a plurality of generating regions formed by upper and lower electrodes on a noncrystalline semiconductor film, such as an amorphous silicon film (hereinafter referred to as an "a-Si film", when applicable), are arranged around one point on the substrate.
The photoelectric conversion efficiency of a solar battery depends mainly on the internal resistance of the solar battery. In particular, it depends on the series resistance of the upper and lower electrodes which are formed on both sides of an a-Si film or the like, and the series resistance of the elongation of the upper and lower electrodes which are brought into contact with each other in order to connect adjacent generating regions.
Heretofore, two methods have been employed to connect the generating regions. In one of the methods, as shown in FIG. 2, a first generating region consisting of a lower electrode 21, and a-Si film 31 and an upper electrode 41, and a second generating region consisting of a lower electrode 22, an a-Si film 32 and an upper electrode 42 are provided on an insulated substrate 1. The first and second generating regions are adjacent to each other, and the upper electrode 41 of the first generating region and the lower electrode 22 of the second generating region are elongated in the direction of arrangement of these regions, so as to be brought into contact with each other. In the other method, as shown in FIG. 3, a lower electrode 21 and an upper electrode 41, and a lower electrode 22 and an upper electrode 42 are provided on an insulated substrate 1. The lower electrode 21 confronts with the upper electrode 41 through an a-Si film 32, and the lower electrode 22 also confronts with the upper electrode 42 through the same a-Si film 32, and the lower electrode 21 and the upper electrode 42 are elongated in a direction perpendicular to the direction of arrangement of the generating area so as to be brought into contact with each other. In the method shown in FIG. 2, the power loss p of the upper and lower electrodes can be represented by the following equation: EQU p=1/3I.sup.2 R(w/x)
where I is the current, R is the sheet resistance of the electrode, x is the length of a generating region, and w is the width of the same.
As is apparent from the equation, if the current and the sheet resistance are constant, the power loss is proportional to the ratio of the width of the generating region to the length of the same. However, in most of the solar batteries for time pieces, as shown in FIG. 4, the total area, the arrangement of generating regions 10, 20, 30, and 40 and the direction of current indicated by the arrows 7 are predetermined. Therefore there is no degree of freedom to determine the ratio of w/x. That is, there is no degree of freedom in design to decrease the power loss in the total area.
Accordingly, it is an object of this invention to eliminate the above-described difficulty accompanying conventional solar batteries for time pieces. More specifically, an object of the invention is to decrease the power loss of the upper and lower electrodes of a solar battery for time pieces, and especially the power loss of transparent electrodes which are high in sheet resistance.
Additional objects and advantages will be set forth in part in the description which follows, and in part will be obvious from the description.